In one-piece polymeric closures, the primary or strongest seal is made by contacting with the outside (an exterior surface) and/or lower part of the outer radius of the finish of a container. Sealing in this location is highly effective at holding internal pressure and preserving the product within the container. One drawback of such a seal is that as the internal pressure increases within the package, the closure begins to dome. This doming pulls the seal geometry radially inward (toward the centerline of the finish opening), which further increases the contact pressure between the closure and these areas of the finish.
If the internal pressure builds within the package, this can lead to potentially undesirable situations. For example, if the package is contaminated and the contents of the package begin to ferment, rather than allowing a safe release of built-up gases, existing closures become stronger and allow pressure to build. When pressure builds to threshold levels, the container may rupture or release from the finish. Both are undesirable situations. Even if the package does not fail in a static state, the package may fail in a dynamic state. For example, when the package is put into a dynamic state (e.g., opening), the closure could still release from the finish due to high internal pressure, which would be undesirable.
It would be desirable to provide a closure that still provides a strong and desirable seal in a one-piece closure, while assisting in preventing or inhibiting pressure to build-up in the package that can lead to potential undesirable conditions.